# Chapter 7 - Quantum Theory and Atomic Structure

Chapter 7 - Quantum theory and Atomic Structure

• To comprehend modern atomic physics, you must first grasp electromagnetic radiation (also called electromagnetic energy or radiant energy).

• The term Electromagnetic radiation refers to including visible light, x-rays, radio waves, and microwaves.

• All of them are made up of energy that is propagated by electric and magnetic forces to grow and decrease in intensity as they travel through space in a wavelike fashion.

• This classical wave model describes how rainbows arise, magnifying glasses operate, and other phenomena such as several additional well-known observations. However, it cannot account for observations on an extremely small scale.

• Three variables and one constant (Figure 7.1) define the wave characteristics of electromagnetic radiation:

• Periodicity (Greek nu). The value represents the frequency of electromagnetic radiation. the number of complete waves, or cycles, that pass through a specific location every second, represented as 1/second [s1; also known as a hertz (Hz)].

• The channel of an FM radio station is the frequency, measured in megahertz (MHz), at which it broadcasts.

• The length of a wave (Greek lambda). The wavelength is the distance between any point on a wave and the equivalent position on the wave's next crest (or trough), or the distance the wave travels in one cycle.

• The term Wavelength refers to being measured in units of meters or, for extremely small wavelengths, nanometers (nm, 109 m), picometers (pm, 1012 m) or angstroms (, 1010 m), a non-SI unit.

• Speed. The speed of a wave is the distance it moves per unit time (meters per second), the product of its frequency (cycles per second), and the wavelength (meters per cycle):

1. Units for speed of wave: cycles/s × m/cycle = m/s

• In a vacuum, electromagnetic radiation moves at 2.99792458×10 m/s (3.00×108 m/s to three significant figures), a physical constant called the speed of light (c):

• c = ν × λ

• Because the product of ν and λ is a constant, they have an inverse relationship— radiation with a high frequency has a short wavelength, and radiation with a low frequency has a long wavelength: ν↑λ↓ and ν↓λ↑

• In Figure 7.1, wave A has a wavelength four times longer than wave C; because both waves are traveling at the same speed, one wavelength of wave A passes a location in the same amount of time as four wavelengths of wave C—the Wave C has a frequency four times that of wave A.

• Intensity. The amplitude of a wave is defined as the height of the crest (or depth of the wave trough).

• The amplitude of an electromagnetic wave is proportional to its intensity the radiation, or in the case of visible light, its brightness.

• A specific hue of light has a particular frequency (and hence a wavelength), but as seen in Figure 7.2, its amplitude can change; the light can be dimmed (lower amplitude, less light).

• In Figure 7.1, wave A has a wavelength four times longer than wave C; because both waves move at the same speed, one wavelength of wave.

• A passes a location in the same amount of time as four wavelengths of wave C—the frequency of wave C is four times that of wave A.

• The height of the peak of a wave is its amplitude (or depth of the trough).

• The amplitude of an electromagnetic wave is proportional to the intensity of the radiation, or brightness in the case of visible light.

• A certain hue of light has a set frequency (and hence wavelength), but as shown in Figure 7.2, its amplitude may vary; the light might be dimmer (lower amplitude, less intense) or brighter (higher amplitude, more intense).

• All electromagnetic radiation waves move at the same speed in a vacuum, but they differ in frequency and, hence, wavelength.

• In the electromagnetic spectrum, the kinds of radiation are organized in increasing wavelength (decreasing frequency) order (Figure 7.3).

• The spectrum, which is a continuum of radiant energy, is divided into regions based on wavelength and frequency, with one area neighboring the next.

• Visible light is only a small part of the spectrum. Distinct wavelengths (or frequencies) of visible light are seen as different hues, ranging from violet (400 nm) to red (750 nm).

• Light with a single wavelength is referred to as monochromatic (Greek for "one color"), but light with many wavelengths is referred to as polychromatic.

• White light is polychromatic because it contains all of the visible light hues. The ultraviolet (UV) radiation (also known as ultraviolet light) area lies close to visible light on the short-wavelength (high-frequency) end; even shorter wavelengths make up the x-ray and gamma () ray sectors.

• Infrared (IR) radiation is found in the region next to visible light on the long-wavelength (low-frequency) end; microwave and radio wave regions are found at even longer wavelengths.

• Some forms of electromagnetic radiation are employed by everyday equipment; for example, microwave ovens, radios, and mobile phones use long-wavelength, low-frequency radiation.

• However, electromagnetic emissions may be found everywhere: from man-made objects like lightbulbs, x-ray machines, and automobile engines to natural sources like the Sun, lightning, radioactivity, and even the sparkle of fireflies!

• Our understanding of the cosmos is based on radiation that reaches our eyes as well as light, x-ray, and radio telescopes.